To elucidate the components of Fraction I of host's red cell extract beneficial for in-vitro cultivation of Plasmodium falciparum and P. knowlesi. To achieve the reinvasion of Aotus red blood cells by P. falciparum merozoites in a plasma-free in-vitro culture system. To continue studies on prolonged in-vitro cultivation of P. knowlesi and P. falciparum. To study the incorporation of nucleic acid precursors into the DNA and RNA of P. falciparum with special reference to the various developmental stages cultured in-vitro.